1. Field of the Invention
The present invention relates to an implantable medical apparatus for detecting diastolic heart failure (DHF), of the type having a DHF determining device for determining at least one blood pressure parameter for detecting a DHF state of the heart of a patient. The invention also relates to a pacemaker provided with such an apparatus, and a method of detecting DHF, including the step of determining at least one blood pressure parameter for detecting a DHF state of the heart of a patient.
2. Description of the Prior Art
There is a growing recognition that congestive heart failure caused by a predominant abnormality in the diastolic function, i.e. diastolic heart failure, DHF, is both common and causes significant morbidity and mortality. Therefore early detection of DHF is important. Patients do not, however, seem to have symptoms at an early stage. In addition it has been hard to separate diastolic and systolic heart failure and they may also exist simultaneously.
It has been discovered that among the few parameters, separating diastolic heart failure from systolic heart failure, are certain blood pressure parameters obtained during work of the patient. Thus U.S. Pat. No. 6,438,408 describes an implantable medical device for monitoring congestive heart failure, CHF. A number of heart failure parameters indicative of the state of the heart failure are measured employing EGMs, blood pressures including absolute pressures, developed pressures (=systolic pressures−diastolic pressures) and the time derivative dP/dt, as well as heart chamber volumes. One of these parameters is the relaxation or contraction time constant τ of the heart chamber. This constant τ is calculated from a continuous pressure signal and is the drop in ventricular pressure at the end of systole and in the first part of diastole. The τ parameter is thus a general parameter reflecting the relaxation process.
Patients suffering from DHF have both elevated ventricular filling pressure and elevated pulmonary venous pressure. To maintain cardiac output under load higher filling pressures are required to achieve adequate left ventricular filling, see H. Weinberger, Diagnosis and Treatment of Diastolic Heart Failure, Hospital Practice, http://www.hosppract.com/issues/1999/03/weinb.htm. However, for DHF patients increased filling pressure does not result in increased left ventricular diastolic volymes. This is illustrated in FIG. 1 which shows results of studies on patients with isolated diastolic dysfunction, see D. W. Kitzman et al, “Exercise Intolerance in Patients with Heart Failure and Preserved Left Ventricular Systolic Function: Failure of the Frank-Starling Mechanism”, J. Am. Coll. Cardiol., 17:1065-1072, 1991. FIG. 1a shows the pulmonary capillary wedge pressure, PCWP, as a function of workload for patients with isolated diastolic dysfunction and for control persons not suffering for this dysfunction, and FIG. 1b shows corresponding curves for the left ventricular end-diastolic volume index, LVEDVI as a function of the workload. From the figures it appears that for patients suffering from the mentioned diastolic dysfunction, PCWP was elevated at rest and further elevated during exercise. This indicates that the ventricular filling pressure was increased under both conditions, whereas LVEDVI did not increase with exercise.